Muscles

Question 1

Type of muscles

Answer 1

Skeletal muscles that are under conscious control

Question 2

Structure of skeletal muscles

Answer 2

Myofibrils formed by a fusion of separate muscle cells
Nuclei is shared among fused cells. Sarcoplasm is a shared cytoplasm that is located at fibrils circumference.

Question 3

Structure of Filament

Answer 3

Tropomyosin- forms a long, thin threads around actin filament.

Myosin- thicker filament made up of fibrous and globular proteins.

Actin- a thinner filament composed of two strands of globular proteins twisted in a helical structure

Question 4

Structure of myosin

Answer 4

Surrounds a head of the filament and the tails are connected together connected.

Question 5

Describe slow-twice muscle fibres

Answer 5

Slow twitch fibres are slow and less powerful but over longer periods of time that create energy from aerobic respiration with a larger store of myoglobin, rich blood supply and lots of mitochondria.

Question 6

What are fast twitch muscles fibres

Answer 6

Move more powerfully but only for short period of time therefore use anaerobic repsiration more often and requires more glycogen, glycolytic enzymes and a store of phosphocreatine (helps generate ATP from ADP)

Question 7

What is a euro muscular junction?

Answer 7

The point where a motor neurone meets a skeletal muscle fibre. Multiple exist to provide rapid and coordinated muscle contractions. A single motor neurone effects several called a motor unit.

Question 8

How is the muscle stimulated

Answer 8

Action Potential Initiation in the neuromuscular junction triggering Ca+2 channels to open.
Acethylcholine-contianing vesicles fuse with the presynaptic membrane. AC diffuses through synaptic cleft.
Receptor binding causes the depolarisation of the muscle cell-surface membrane

Question 9

Muscle Contraction Process

Answer 9

Action potential travels through cell-surface membrane then into the sacroplamic reticulum releasing Ca+2 init sarcoplasm causing tropomyosin to expose binding sites on actin filament. Myosin head attached with an ADP binds to exposed sites. Myosin head changes angle pulling actin filament causing ADP to be released. ATP binds to myosin head, causing it to detach from actin. Calcium activates ATPase hydrolysing ATP into ADP and Pi releasing energy to reset the myosin head position. Myosin head binds to the next actin filament and process repeats.

Question 10

Muscle Relaxation

Answer 10

Neverous Impulse triggers active transport of Ca+2 ions from the sacroplasm back into the sarcoplasmic reticulum causing the tropomyosin to cover the filament binding site causing muscle fibres to return to resting state.

Question 11

During vigorous exercise, the pH of skeletal muscle tissue falls. This fall in pH leads to a reduction in the ability of calcium ions to stimulate muscle contraction.
Suggest how.

Answer 11

2. Fewer calcium ions bind to tropomyosin;
   Accept troponin
3. Fewer tropomyosin molecules move away;
4. Fewer binding sites on actin revealed;
5. Fewer cross-bridges can form

Question 12

Describe the roles of calcium ions and ATP in the contraction of a myofibril.

Answer 12

(Calcium ions) cause movement of tropomyosin (on actin);
3. (This movement causes) exposure of the binding sites on the
actin;
4. Myosin heads attach to binding sites on actin;
5. Hydrolysis of ATP (on myosin heads) causes myosin heads to
bend;
6. (Bending) pulling actin molecules;
7. Attachment of a new ATP molecule to each myosin head
Low pH changes shape of calcium ion receptors
Do not accept tropomyosin does not move
Calcium ions diffuse into myofibrils from (sarcoplasmic) reticulum;
causes myosin heads to detach (from actin sites).

Question 13

What is the role of ATP in myofibril contraction?

Answer 13

Provides energy to move myosin head;
(Reaction with ATP) breaks/allows binding of myosin to actin/ actinomyosin bridge;